This invention generally relates to automatic typewriters and, more particularly, to a unit for sensing tabulation operations in such automatic typewriters.
Automatic typewriters are used in automated typing, computer, message transfer and other systems and applications. In such systems, these typewriters perform a data input and transmitting function and a signal receiving and data output function. During the first function an operator strikes the typewriter keys simultaneously to type on that typewriter, and, by means of various sensors, to transfer to signal processing equipment signals representing the typing operations being performed. In an automated typing system, this equipment comprises circuits for transferring the signals to a storage medium; in a computer system, a computer or an input/output controller; and in a message transfer system, another automatic typewriter.
During the signal receiving and data output function, the signal processing equipment transfers character and timing signals to the automatic typewriter. Various actuators cause the typewriter to print in response to these received signals.
A number of such automatic typewriters have been and are now available. They have become more popular with the advent of code responsive, bail operated, electric typewriters. Such typewriters are marketed by IBM under the trademark "Selectric." These electric typewriters are sold both to offices for use as conventional electric typewriters and to other manufacturers for use as automatic typewriters in the foregoing and other applications.
One operation which all typewriters perform is a tabulation. Conventionally an operator strikes a tab key in a code responsive, bail operated typewriter to pivot a tab torque bar, and move backspace and escapement pawls out of racks. A tensioned mainspring then unwinds and, through a pulley network, moves a carrier until a tab lever contacts a tab stop. An automatic typewriter must also perform this operation in response to signals from the signal processing equipment. Moreover, the signal processing equipment must not transmit signals corresponding to subsequent operations until the tabulation operation is completed.
There are several possible ways to inhibit the transmission of such signals. For example, the signal processing equipment might delay the issue of any further signals for a fixed, instant interval corresponding to the maximum tabulation operation interval. As many such operations are only for a few spaces (e.g., the indentation of a paragraph) this constant delay after each tabulation operation can reduce the effective typing rate noticeably, especially where a line is typed after multiple tabulation operations.
There are two alternate procedures for sensing the actual time the tabulation operation occurs, which do improve overall typing speeds. In one a sensor, transmits signals in response to motion of the tab torque bar. However, the resulting signals are not very reliable because the tab torque bar undergoes damped oscillations at the beginning and end of each tabulation operation. The sensors can produce multiple signals during these oscillations and cause the signal processing equipment to respond erroneously.
In another unit, a fluid clutch connects to a shaft from the mainspring. During a tabulation operation, the shaft rotates an impeller in the fluid clutch and displaces a magnet, carried by an arm on the outer housing of the fluid clutch, into proximity with a magnetically operated switch thereby to close the switch. Although this sensing unit substantially eliminates the erroneous signals produced in the tab torque bar sensing unit, the conventional mainspring either must be replaced or must be modified because the conventional mainspring has no such mainspring shaft.
Therefore, it is an object of this invention to provide simplified tabulation sensing unit.
Another object of this invention is to provide a simplified fluid clutch tabulation sensing unit which utilizes a conventional mainspring.
Yet another object of this invention is to provide a tabulation sensing unit which is less expensive than prior units.